History
The VAX-11 minicomputer architecture was introduced in the late 1970s by Digital Equipment Corporation (DEC). DEC was a massive player in the computer industry during the era of the mini-computer; unfortunately, a series of bad decisions and the advent of the PC slowly (but surely) led to their demise“The Innovator’s Dilemma” by Clayton M. Christenson. Harper Paperbacks, January 2003. A fantastic book about the disk-drive industry and how new innovations disrupt existing ones. A good read for business majors and computer scientists alike. Provides insight on how large and successful companies completely fail.. The architecture was realized in a number of implementations, including the VAX-11/780 and the less powerful VAX-11/750.
The OS for the system was known as VAX/VMS (or just plain VMS), one of whose primary architects was Dave Cutler, who later led the effort to develop Microsoft’s Windows NT“Inside Windows NT” by H. Custer, D. Solomon. Microsoft Press, 1993. The book about Windows NT that explains the system top to bottom, in more detail than you might like. But seriously, a pretty good book.. VMS had the general problem that it would be run on a broad range of machines, including very inexpensive VAXen (yes, that is the proper plural) to extremely high-end and powerful machines in the same architecture family. Thus, the OS had to have mechanisms and policies that worked (and worked well) across this huge range of systems.
As an additional issue, VMS is an excellent example of software innovations used to hide some of the inherent flaws of the architecture. Although the OS often relies on the hardware to build efficient abstractions and illusions, sometimes the hardware designers don’t quite get everything right. In the VAX hardware, we’ll see a few examples of this, and what the VMS operating system does to build an effective, working system despite these hardware flaws.